1. Field of the Invention
This invention relates to the construction of poured-in-place concrete structures, and is particularly directed to a method of concurrently carrying out the several steps of erecting formwork, laying in reinforcement, pouring fresh concrete into the formwork, curing the concrete members so formed, and stripping the formwork from the cured concrete members. Phrased otherwise, this invention is directed to a method of construction in which formwork is erected for several stories above the last completed story of the building under construction, so that the various steps mentioned above can be carried out concurrently on different respective stories, thereby effecting savings in workman waiting time and in total building erection time.
2. Brief Description of the Prior Art
Conventional cast-in-place construction of a typical concrete multi-story building requires that the slab for each floor level be formed and poured before formwork for the vertical structural members (i.e., columns and bearing walls) leading to the next floor level can be erected, and thereby creates timing conflicts and delay periods among the various tasks involved. For example, in a standard eight-day cycle (i.e., eight working days being required for each story) concrete is poured only two days of the eight (one day for the floor slabs, one day for the walls and columns). By the very nature of the standard method, workmen such as electricians, plumbers, and cement finishers are continually interrupted. Consequently the standard method of construction is rather inefficient and leaves considerable room for improvement. Nonetheless, no suitable method for improving the efficiency of construction has previously been offered.
In the conventional method of constructing a reinforced concrete high rise building (indeed in any known method), the speed with which one floor cycle is completed depends on the quantity of forms used, the complexity of the building structure, the availability of manpower, the number of hours worked, the coordination and cooperation of the tradesmen and subcontractors involved, the contractor's scheduling process, weather, the owner's requirements, inspection time, and curing time of the concrete.
These conditions impose themselves upon a structure and dictate its speed of construction. For example, if it takes eight working hours to erect a slab form for a particular building, that is the minimum amount of time which must be devoted to that step. The sum of the times required for the various steps of the construction method dictates the floor-to-floor cycle time, taking into consideration normal overlap of some operations. One example of overlap is that conduit can be placed at one end of one story of a building while the bottom reinforcement steel is still being placed in other areas of that same story. This overlapping is standard procedure with time-oriented building contractors and is a prime consideration in scheduling.
All known construction methods require placing the column steel reinforcement and column formwork for each floor only after concrete for the next prior floor has been poured. This is the traditional beginning point for the next cycle and is the standard method of construction for a poured-in-place reinforced concrete structure. Regardless of the speed of the floor-to-floor cycle, the sequence remains the same.
Depending on the complexity of the structure for a given building, the performance of all the work necessary for one floor-to-floor cycle consumes from three to ten days. For the work required for the construction to progress one story (e.g., from the fourth floor to the fifth floor of a building), the sequence of steps is generally as outlined:
Step No. 1--Pour slab (assume 4th floor). PA1 Step No. 2--Install vertical reinforcing steel. PA1 Step No. 3--Erect formwork for columns and walls to 5th floor. PA1 Step No. 4--Pour columns and walls. PA1 Step No. 5--Strip vertical formwork. PA1 Step No. 6--Erect deck formwork for 5th floor slab. PA1 Step No. 7--Place reinforcing steel and conduits. PA1 Step No. 8--Pour 5th floor slab (Step No. 3 is sometimes combined with this step). PA1 Friday, Step No. 1; PA1 Monday, Steps No. 2, 3, and 4; PA1 Tuesday, Step No. 5 and 6; PA1 Wednesday, Step No. 7; PA1 Thursday, Step No. 8;
Typically these steps could fall on calendar days as follows:
This constitutes what is known as a four-day cycle, which is considered to be the standard of good practice.
In this conventional method, at any one time there is formed only the next slab to be poured, other than the formed slabs curing below. Up to three full slab forms are used for a building, depending on the curing time required prior to stripping or removal of the slab form, and also depending on the speed desired during construction.
In the standard conventional method, deck forms are never installed above unpoured slabs, and any column forms are erected only for the columns rising directly to the next floor slab to be poured, and never for any stories above that floor.
Further, field engineering crews are required to lay out the decking formwork for each slab to compensate for elevational errors in the slab therebelow. In a normal slab, these elevational differences are typically 1/4 inch. It is necessary for these crews to do layout work on each freshly poured slab and also to lay out column alignments and level the decking formwork. Thus, two engineering work elements are required per slab. Without releveling of the slab forms by the field engineering crews, the variances would accumulate, and the top stories of a high-rise building could be unintentionally offset from their design height by several inches.
Desirably, in order to erect formwork several stories above an unpoured floor slab, some means would be required to ensure that the poured slabs for each story would automatically be adjusted to the proper elevation. Also, some means would be necessary to control the formwork dimensional layout. However, no such means has been available. Further, it has never been previously proposed to erect formwork over an unpoured slab.